This invention relates to a velocity control method for an elevator, and more particularly to a velocity control method in which the delay time of the response of a control system need not be manually adjusted.
FIG. 4 is a schematic constructional view, partly in blocks, showing elevator equipment in which a prior-art elevator velocity control method disclosed in, for example, the official gazette of Japanese Patent Application Publication No. 22671/1986 is performed. Referring to the figure, numeral 1 designates a three-phase A.C. power source, numeral 2 a thyristor converter whose input side is connected to the three-phase A.C. power source 1 and which converts a three-phase alternating current into a direct current, and numeral 3 the armature (the field system being omitted) of a hoisting D.C. motor which is connected to the output side of the thyristor converter 2. Also included in the elevator equipment are the sheave 4 of a hoist, which is coupled to the shaft of the armature 3 and which is driven by this armature 3, a main cable 5 which is wound round the sheave 4, a cage 6 which is joined to one end of the main cable 5, a counterweight 7 which is joined to the other end of the main cable 5, a rope 8 in an endless shape, both the ends of which are spliced to the cage 6, a tightening pulley 9 which is arranged at the lower part of an elevator shaft (not shown) and which applies a tension to the rope 8 wound round it, and a disc 10 which is installed in an elevator machinery room (not shown), round which the rope 8 is wound and which has its circumferential part formed with apertures 10a at equal intervals. A pulse generator 11 is arranged in opposition to the circumferential part of the disc 10, and it generates a pulse each time the aperture 10a is detected. An add/subtract counter 12 adds the pulses during the ascent of the cage 6 and subtracts them during the descent, thereby to count the current position of the cage 6. The first input converter 13 converts the output of the add/subtract counter 12 into information for an electronic computer. The elevator equipment further includes the central processing unit (hereinafter, abbreviated to "CPU") 14 of the electronic computer, buses 15 such as an address bus and a data bus by which the first input converter 13 and CPU 14 mentioned above and devices to be stated below are interconnected, a read-only memory (hereinafter, abbreviated to "ROM") 16 in which programs for controlling the cage 6, velocity command values corresponding to the variation of a distance, are kept written, and a random access memory (hereinafter, abbreviated to "RAM") 17 which stores data in its storing addresses. Also included are an output converter 18 by which information from the electronic computer is converted into a signal for the elevator device, a tachometer generator 19 which is coupled to the shaft of the armature 3 and which generates a velocity signal corresponding to the velocity of the armature 3 when driven by this armature, and a velocity controller 20 which is connected to the output sides of the output converter 18 and the tachometer generator 19 and which controls the thyristor converter 2 thereby to control the velocity of the hoisting D.C. motor. Numeral 21 indicates call signals which are generated when calls have occurred, and numeral 22 a call registration circuit which registers the calls when supplied with the call signals 21. The second input converter 23 converts the output of the call registration circuit 22 into information for the electronic computer, while the third input converter 24 converts the output of the tachometer generator 19 into information for the electronic computer.
Next, the operation of the elevator equipment shown in FIG. 4 will be described with reference to a flow chart in FIG. 5. Numerals 100-114 in FIG. 5 indicate the operating steps of the elevator equipment in FIG. 4.
At the step 100, the call signal 21 is generated, and the output of the call registration circuit 22 is accepted into the CPU 14 through the second input converter 23. At the step 101, the traveling direction of the cage 6 is discriminated on the basis of the current position thereof, and at the step 102, a start command is given by the CPU 14. At the step 103, the first velocity command value V.sub.p1 which increases with the lapse of time is generated for a high-speed travel by way of example, and it is transmitted from the ROM 16 to the velocity controller 20 through the output converter 18, whereby the armature 3 of the motor is started. Meanwhile, at the step 104, a deceleration distance (advance magnitude) which is required for the cage 6 to be capable of stopping with a good riding quality is calculated by the CPU 14. Subsequently, the step 105 determines a call, namely, a floor to stop at, which is distant in excess of the advance magnitude.
Now, when the armature 3 is started, the cage 6 begins to move through the sheave 4 as well as the main cable 5. A velocity signal corresponding to the velocity of the armature 3, in other words, the velocity of the cage 6, is issued from the tachometer generator 19. This velocity signal is accepted into the CPU 14 through the third input converter 24 and is differentiated therein, and it is simultaneously compared in the velocity controller 20 with the first velocity command value V.sub.p1 generated at the step 103, whereby the velocity of the cage 6 is automatically controlled at high precision. Meanwhile, the movement of the cage 6 is transmitted to the disc 10 through the rope 8, and the disc 10 is therefore rotated, whereby the pulse generator 11 generates the pulses. These pulses are added or subtracted by the add/subtract counter 12, and the result is accepted through the first input converter 13 into the CPU 14, in which the current position of the cage 6 is calculated from the movement distance thereof. In consequence, a residual distance S for a point H (shown in FIG. 6 to be referred to later) which indicates the floor scheduled to stop at is calculated by the step 106. The residual distance correction of adding a corrective distance K to the residual distance S is made by the step 107.
Here, the elevator velocity control method in the prior art will be described with reference to FIG. 6. This figure shows a diagram of velocity command value curves in which the response delays of a control system are considered. Referring to the figure, symbol V.sub.p denotes the situation of a velocity command value which changes with the lapse of time during the acceleration of the cage 6, and in which symbol V.sub.p1 indicates the first velocity command value during the high-speed travel (long-distance travel) of the cage 6, while symbol V.sub.p2 indicates the first velocity command value during the low-speed travel (short-distance travel). On the other hand, symbol V.sub.d denotes the situation of the second velocity command value which decreases in correspondence with the residual distance S from the current position of the cage 6 to the point H indicative of the floor scheduled to stop at, during the deceleration of the cage 6. In addition, symbol V.sub.t1 denotes that actual velocity of the cage 6 which delays for a time interval T.sub.1 relative to the first velocity command value V.sub.p1. Likewise, symbol V.sub.t2 denotes that actual velocity of the cage 6 which delays for the time interval T.sub.1 relative to the first velocity command value V.sub.p2.
In the case where the cage 6 follows up the velocity command value V.sub.p with the predetermined time delay T.sub.1, the first velocity command V.sub.p1 which is advanced for the time interval T.sub.1 relative to the cage velocity V.sub.t1, for example, needs to be delivered as the output of the velocity command value V.sub.p in order that the cage 6 may be run with an aim at the point H indicative of the floor scheduled to stop at. In the high-speed travel mode, the first velocity command value V.sub.p1 increases from a start point O.sub.1 and reaches a point H.sub.1 through a point A.sub.1 corresponding to a velocity command value V.sub.11. At the point H.sub.1, a change-over preparation command is issued. Meanwhile, the actual velocity V.sub.t1 of the cage 6 and the second velocity command value V.sub.d are always compared. When the values V.sub.t1 and V.sub.d become equal at a point F.sub.1, the second velocity command value is changed-over from the value V.sub.d to a value V.sub.d2. As a result, the velocity command value V.sub.p traces a path O.sub.1 -A.sub.1 -H.sub.1 -H. Thus, the velocity of the hoisting D.C. motor, namely, that of the cage 6 is controlled according to this velocity command value V.sub.p.
As described before, when the call has occurred during the travel of the cage 6, the residual distance S from the current position of the cage 6 to the scheduled stopping position H is calculated every moment. At a time B.sub.1 by way of example, the residual distance S is expressed by the area of a region B.sub.1 -C.sub.1 -F.sub.1 -H-B.sub.1. Here, the point C.sub.1 corresponds to the value of the actual velocity V.sub.t1 at the time B.sub.1. The corrective distance K is expressed by the area of a region C.sub.1 -G.sub.1 -F.sub.1 -C.sub.1. Here, the point G.sub.1 corresponds to a velocity command value V.sub.13. Assuming the waveform of an acceleration as shown in FIG. 7, the corrective distance K is evaluated in accordance with -a/2 (2 T.sub.1.sup.2 +2 T.sub.1 (2 T+T.sub.c) +8/3 T.sup.2 +T.sub.c.sup.2 +3 T T.sub.c). Here, "a" denotes the maximum acceleration, "-a" the maximum deceleration, "T" a jerk time, and "T.sub.c " a constant-speed travel time, T.sub.c .gtoreq.T.sub.1 being held.
Subsequently, the second velocity command value V.sub.d for the corrected residual distance (S+K) is extracted from within the ROM 16 by the step 108 in FIG. 5. At the time B.sub.1, the distance corresponding to (S+K) is expressed by the area of a region B.sub.1 -G.sub.1 -F.sub.1 -H-B.sub.1. The extracted second velocity command value V.sub.d and the first velocity command value V.sub.p1 are compared at the step 109. When (V.sub.d -V.sub.p1) .ltoreq.(a prescribed value) at the time B.sub.1, the change-over preparation command (a curve A.sub.1 -H.sub.1 in FIG. 6) is issued at the step 110a. Besides, at the step 110b, the residual distance correction is suspended, and the second velocity command value V.sub.d corresponding to the residual distance S is extracted from the ROM 16, whereupon at the step 110c, the second velocity command value V.sub.d2 delayed for the time interval T.sub.1 is obtained by subtracting a T.sub.1 from V.sub.d. The step 111 compares the first velocity command value V.sub.p1 and the second velocity command value V.sub.d2, and when V.sub.p1 .gtoreq.V.sub.d2 has held, the step 112 changes-over the first velocity command value V.sub.p1 to the second velocity command value V.sub.d2 at the point H.sub.1. Thenceforth, the second velocity command value V.sub.d2 decreases, and the cage 6 is decelerated accordingly. When the completion of the floor arrival of the cage 6 is acknowledged at the step 113, the cage 6 is stopped at the step 114.
The low-speed travel mode proceeds similarly. The second velocity command value V.sub.d for the corrected residual distance (S+K) is extracted from within the ROM 16. The extracted second velocity command value V.sub.d and the first velocity command value V.sub.p2 are compared, and when (V.sub.d -V.sub.p2).ltoreq.(a prescribed value) has held, a change-over preparation command is issued. At a point H.sub.2 at which V.sub.p2 .gtoreq.V.sub.d2 holds, the first velocity command value V.sub.p2 is changed-over to the second velocity command value V.sub.d2.
With the prior-art elevator velocity control, even in a case where the delay time is varied by a rotary switch or the like for adjusting the riding quality of the cage, there is the problem that the adjustments are difficult and require a skilled technique. Moreover, since the respective cages exhibit different delay times, the adjustments for the individual cages are troublesome. Besides, since the delay time varies depending upon the conditions of the respective travels, the riding quality worsens in any travel when the delay time is fixed.